Journal of Cytology

: 2011  |  Volume : 28  |  Issue : 3  |  Page : 124--126

The mystic thyroid nodule: A cytologist's confront

HR Vanisri, K Vani, CS Sheela Devi, R Sunila 
 Department of Pathology, JSS Medical College, A Constituent College of JSS University, Mysore, India

Correspondence Address:
H R Vanisri
59/D5, 2nd Main 2nd cross, Yadavgiri, Mysore - 570 020


Metastatic thyroid carcinoma is clinically silent and found only at autopsy in most instances. Renal cell carcinoma (RCC) is the most common and constitutes 56% of all secondary malignancies. However, preoperative distinction between primary and secondary thyroid neoplasms is often challenging. Fine needle aspiration is helpful in establishing a correct preoperative diagnosis. A local surgical resection is curative if prompt preoperative diagnosis is established. We hereby report a case of isolated metastatic RCC to the thyroid in a 65-year-old woman, diagnosed by fine needle aspiration cytology and later confirmed with histopathological examination.

How to cite this article:
Vanisri H R, Vani K, Sheela Devi C S, Sunila R. The mystic thyroid nodule: A cytologist's confront.J Cytol 2011;28:124-126

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Vanisri H R, Vani K, Sheela Devi C S, Sunila R. The mystic thyroid nodule: A cytologist's confront. J Cytol [serial online] 2011 [cited 2022 Dec 6 ];28:124-126
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Preoperative fine needle aspiration has been an effective tool in differentiating primary and secondary thyroid carcinomas. The presence of nests of clear cells with distinct borders, compact dark nuclei and extensive vascularity should increase the suspicion of metastatic renal cell carcinoma (RCC). The differentiation can be achieved best with thyroglobulin antibody immunohistochemical staining. It is positive in primary thyroid tumors and negative in metastatic tumors. [1] The thyroid gland is a rare site of metastasis. [2] In one study metastatic cancers in the thyroid accounted for 0.1% of all thyroid nodular lesions that were investigated by fine needle aspiration. [3] Clinically recognized metastasis to the thyroid is much less common than metastasis found at autopsy. [1] The overall incidence varies from 1.25% in unselected patient autopsy series to 24% in autopsies of patients with widespread malignant neoplasms. [4] RCC is the most common, constituting 56% of all secondary malignancies. [4]

In clinical and autopsy series performed in Europe and US, breast carcinoma, lung carcinoma and melanoma are the most frequent source of metastasis to the thyroid gland. [2],[4] Adenoid cystic carcinoma in a thyroid nodule from an unknown primary has been reported. Awareness and knowledge of occurrences of these lesions will help in making a correct diagnosis in cytology. [5]

We report a case of isolated thyroid metastasis from RCC, 3 years after nephrectomy without local recurrence or metastasis to other organs.

 Case Report

A 65-year-old woman presented with a palpable mass in the left neck region of 20 days duration. Patient had no other symptoms such as dyspnea, hoarseness of voice or dysphagia. Her medical history included right radical nephrectomy for RCC, 3 years previously. Patient required no adjuvant therapy after radical nephrectomy.

Physical examination revealed a 3 × 4 cm hard, nontender mass without associated palpable cervical lymph node enlargement. Her complete blood count, electrolyte and thyroid function tests were within normal range. She underwent fine needle aspiration cytology of this nodule. Cytology showed cellular smears displaying sheets of polygonal cells with centrally placed nuclei. Cytoplasm was moderate to abundant and vacuolated [Figure 1]. Normal thyroid follicular cells were also noted. Impression of secondary deposit in the thyroid from primary RCC was made. Patient underwent right hemithyroidectomy. Grossly, the specimen measured 4 × 4 × 3 cm and cut section showed a well circumscribed grey white nodule measuring 4 × 3 cm. Normal tan brown thyroid tissue was noted at the periphery [Figure 2]. Histology sections displayed a well encapsulated tumor with sheets of polygonal cells having clear cytoplasm and centrally placed nucleus. Traversing capillaries were noted. Normal thyroid follicles were seen outside the capsule [Figure 3]. A diagnosis of metastatic RCC to the thyroid was made. On immunohistochemistry, the tumor cells were positive for vimentin and CD10 (focal) and negative for CK-19, thyroglobulin and thyroid transcription factor-1 (TTF-1). Patient continues to remain disease free after hemithyroidectomy, with no further evidence of any other metastasis or local recurrence.{Figure 1}{Figure 2}{Figure 3}


Thyroid metastasis is a rare event in clinical practice. [2] Secondary malignancies are thought to constitute <1% of thyroid cancers. [3] At autopsy, thyroid metastasis range from 1.9 to 24.2%, suggesting that unrecognized metastasis to the thyroid is more common than clinically recognized disease. [6] However, of the clinically recognized metastasis to the thyroid gland, more than 50% of the time the culprit is RCC and the incidence of metastatic RCC to the thyroid is as high as 78%. [1] The first report of thyroid metastasis from primary RCC was reported in 1891. [6] Thus, RCC is by far the most common source of clinically relevant metastasis to the thyroid gland. In the literature, there are only case reports describing RCC metastatic to the thyroid. A pre-operative diagnosis of secondary thyroid tumors is difficult due to the rarity, long interval between the onset of renal primary and detection of thyroid metastasis. In the present case, positive medical history of RCC 3 years back and preoperative thyroid fine needle aspiration cytology findings of nests of clear cells aided in establishing a diagnosis of secondary metastatic RCC in the thyroid. Development of thyroid mass in a patient previously treated for RCC (or any other tumor), even many years earlier, should arouse suspicion of metastasis. [2] Earlier studies have shown statistics exemplifying excellent prognosis for RCC with isolated thyroid metastasis and importance of surgical resection. [1]

It is difficult to distinguish metastatic RCC from primary lesions of thyroid, such as anaplastic carcinoma or the clear cell variant of follicular carcinoma. [7] RCCs and thyroid follicular epithelial neoplasms with clear cells may have a variety of histologic patterns that make a distinction on morphologic grounds alone difficult. RCCs may have pseudofollicles filled with blood. The cells have clear cytoplasm, distinct boundaries and small, compact, dark nuclei. Thyroid follicular epithelial tumors with clear cells are rare and include follicular adenoma, follicular carcinoma and papillary carcinoma. The clear cell component within a primary thyroid follicular neoplasm may be the dominant cell type or may represent a minor component of the entire neoplastic proliferation. The presence of clear cells in any thyroid follicular neoplasm does not alter the overall prognosis of that particular tumor type. [8] Clear cell change itself may be difficult to identify on FNAC. In contrast with tissue, the cytoplasm is not always optically clear in cytology specimens. [9]

Immunohistochemical stain for TTF-1 represents a specific marker for tumors originating from follicular cells of thyroid. There seems to be no radiological features to differentiate primary and secondary malignancies. Sonographically guided fine needle aspiration or biopsy could be useful for diagnosing metastasis to the thyroid gland. [4] The spread of RCC to the thyroid appears to be hematogenous, possibly by bypassing the lungs. [1] There is no clear consensus about the choice of surgical procedure (lobectomy or total thyroidectomy), but several studies report that long-term survival can be achieved with total thyroidectomy because of multifocality of the lesions. [2] Some authors recommend lobectomy and isthmectomy. [1] Surgical resection is regarded as the best treatment for metastatic thyroid tumor, especially if primary carcinoma has been resected with no signs of metastasis elsewhere. Postoperative treatment with interferon is recommended in subjects with thyroid metastasis from RCC. It has been reported to result in prolonged survival without any evidence of recurrence in 10% patients with isolated thyroid metastasis. The prognosis is worse in patients presenting with widespread metastasis. [2]


RCC is a unique tumor that can present as metastasis to the thyroid years after nephrectomy. A presurgical diagnosis of secondary thyroid tumors is relatively difficult because there are no specific clinical or radiological features. FNAC has an indispensible role in preoperative diagnosis and workup in patients presenting with thyroid mass and a medical history of RCC. If metastatic RCC is linked to the thyroid gland, only surgical intervention can be curative.


We acknowledge the guidance of Dr. Manjunath GV, Prof. and HOD Department of Pathology, JSS Medical College, a constituent college of JSS University, Mysore.


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